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Q641. What are the changes in Java 9 ?

Ans. JVM and JDK are getting smaller.

New command line tool called jshell that will add native support and popularize a Java way to REPL (Read-Eval-Print-Loop)

private methods in interfaces

Introduction of the module system or project Jigsaw

JavaDoc Search

Light version of JSON API

HTTP2 client

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Q642. If an Abstract class has only abstract methods, What's the difference between such a class and an interface ?

Ans. Such a class still can have member elements which can be inherited and hence facilitate code reuse. Moreover Abstract class can have non final static elements whereas interfaces are only allowed to have static final elements.

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Q643. What are some uses of interceptors ?

Ans. Authentication / Authorization
URL forwarding
Auditing / Logging
Localization

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Q644. Why is goto not used in Java?

Ans. Goto statement results in unstructured jumps in control from one code location to another and hence makes the code very difficult
to read , maintain and debug. Moreover Goto can always be replaced using other statements like break / continue and hence results in structured movement of programming control.

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Q645. Are Annotations better than using XML configs ?

Ans. Yes , as both code and its meta information reside in the same file, it promotes better readability and maintenability.

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Q646. What is the use of Annotations in Java ?

Ans. Annotations are used to specify meta information about the code.

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Q647. Can we deploy an application to server using a jar file ?

Ans. Conventionally we need a WAR file to be deployed to server. Though with Spring Boot we can even deploy using jar.

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Q648. Write a Program to convert a binary to number ?

Ans. int convert(int binaryInt) {
int sumValue=0;
int multiple = 1;
while(binaryInt > 0) {
binaryDigit = binaryInt;
binaryInt = binaryInt /10;
sumValue = sumValue (binaryDigit * multiple);
multiple = multiple * 2;
}

return sumValue;
}

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Q649. Write a multi threaded Program that will simulate transferring of money across accounts ?

^{This question was recently asked at 'Trustwave'.This question is still unanswered. Can you please provide an answer.}

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Q650. Which component of MVC you like to work on ?

^{This question was recently asked at 'CapTech'.This question is still unanswered. Can you please provide an answer.}

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Q651. Write a class and override the equals and hashcode method ?

Ans. class Student
{
///
///
///
private int id;
private String name;

///
///
///
public Student(int id, String name)
{
this.name = name;
this.id = id;

}// Student

///
///
///
public int getId()
{
return id;

}// getId

///
///
///
public void setId(int id)
{
this.id = id;

}// setId

///
///
///
public String getName()
{
return name;

}// getName

///
///
///
public void setName(String name)
{
this.name = name;

}// setName

@Override
public boolean equals(Object obj)
{
if (obj == null) return false;
if (!(obj instanceof Student))
return false;
if (obj == this)
return true;

return this.getId() == ((Student) obj).getId();

}// equals

///
///
///
@Override
public int hashCode()
{
return this.getId();

}// hashCode

}// Student

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Q652. How does java identifies which method to be called in method overriding or runtime polymorphism, when both methods share the same name and signature ?

Ans. Java identifies the method to be called at runtime by the object that is being referenced.

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Q653. Which of the two - compile time and run time polymorphism - requires signature of the method to be different ?

Ans. runtime polymorphism or method overriding doesn't require method name and signature to be different whereas compile time polymorphism or method overloading requires method name to be same but the signature to be different.

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Q654. How can you extract integers from string values and add (sum it up) all the extracted integers? e.g "James34long4island322in3rdAvenue" ---> 34 4 322 3 = 363

^{This question was recently asked at 'Horizon Solutions'.This question is still unanswered. Can you please provide an answer.}

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Q655. How is garbage collection in Java 8 different from Java 7 ?

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Q656. What is the use of java.util.concurrent package in Java ?

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Q657. What is the difference between keywords, identifiers and literals in java ?

Ans. Keywords are the reserved words that have a pre defined meaning for the compiler and hence are restricted to be used as identifiers.

Identifiers are the name assigned to different programming constructs like classes, interfaces, methods , variables etc.

Literals are the values that are assigned to Identifiers.

For example

int count = 0;

in the above statement "int" is a keyword, "count" is an identifier and "0" is a literal

Sample Code for keywords

Sample Code for identifiers

Sample Code for literals

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Q658. What are the some literals in java that are reserved and hence cannot be used as identifiers ?

Ans. true , false and null

Sample Code for literals

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Q659. Can we use true and false as identifiers in java ? Are they keywords in Java ?

Ans. true and false are literals in java. No we cannot use them as identifiers.

Sample Code for literal

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Q660. What is the importance of Abstract Class ?

Ans. Abstract classes provide a mechanism of interfacing ( using abstract method ) as well as code reuse through inheritance ( extending abstract class )

Comparing to concrete class they have an advantage of providing interface which a concrete class doesn't provide.

Comparing to interfaces they have an advantage of providing code reuse through inheritance which interfaces dont provide.

Sample Code for abstract class

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Q661. Can we use java keywords as identifiers ?

Ans. No, keyword has pre defined meaning for compiler and hence cannot be used as identifiers.

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Q662. What is a difference between Identifier and keyword ?

Ans. Keyword is a reserved word that has a pre defined meaning for the compiler and hence cannot be used as an identifier, for example - final, private , for etc.

Identifier is the name given by the programmer to a programming construct, for example - class and method names etc.

java Keywords cannot be used as an identifier in java.

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Q663. Which of the following applies to "private"?

It is a keyword
It is a modifier
It is an access modifier

Ans. Yes, all of them applies to private keyword. It is an access modifier.

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Q664. Which of the following applies to Final ?

It is a keyword
It is a modifier
It is an access modifier

Ans. It is a keyword and a modifier but not an access modifier.

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Q665. What is the difference between a keyword and a modifier ?

Ans. Keywords are the reserved words that have a pre defined meaning for a compiler whereas modifiers are the type of keywords that modifies the state or definition of a programming construct.

for, while are keywords but not modifiers.
private , public , final , abstract etc are keywords as well as modifiers.

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Q666. What are access and non access modifiers ?

Ans. Access modifiers are the java reserved keywords that changes the access privileges on a class , method , element etc. For example - public , private and protected.

Non Access modifiers are the java modifiers other than access modifiers. For example - static , final, abstract, synchronized, transient, volatile etc.

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Q667. Is synchronized a keyword , modifier, identifier? what is it ?

Ans. synchronized is a keyword and a modifier. The synchronized keyword is used to indicate that a method can be accessed exclusively by one thread at a time.

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Q668. In Java, if object A contains same the same data of object B, are they equal?

Ans. it depends on the implementation of equals method of the respective class. If no definition is provided and it uses the default definition of the object class, two references are equal only if they point to the same object.

We can have such an equality defined for a particular class objects if we provide appropriate implementation of equals method comparing all those fields.

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Q669. Difference between void and return ? Can we have return statement in the void method ?

Ans. void is a declaration that states that the method declared void is not expected to return anything.

return is a statement within the method that returns the control out of the method.

Yes, we can have return statement in the void method but without any argument.

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Q670. Explain OOPS.

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